For your 72 kg weight, a sail size between 8.5 and 9.5 should be fine to start and sustain the planing as of 10 knots of wind on a 76 cm wide board + 48 cm fin combo.

With a Futura, either a Severne NCX no cams 9.0 m2 or an Overdrive 3 cams 8.6 or 9.5 m2 sail is a perfect match to the board's plug & play character, no need to take a full-on racing sail à la Reflex...

They are not to small but it's depend what you want to do. With your weight it will be better NCX 9.0 & 8.0 except if you live in a very windy place.
I am 93kgs and 9.0 work very well on it with the NCX.

They are not to small but it's depend what you want to do. With your weight it will be better NCX 9.0 & 8.0 except if you live in a very windy place.
I am 93kgs and 9.0 work very well on it with the NCX.